For decades it's been said that the sonic screwdriver is harmless. And for decades, that was the case. But it appears that could be changing. Sure, it's been used to threaten people in the past, but it's always been an indirect threat. The Fourth Doctor,for instances, threaten to detonate the explosives he had placed on Davros' travel machine.
But that used to be the extent of the non-harmless nature of the sonic screwdriver.
But in the relaunch, that seems to have changed. Not immediately, but there are instances that point to it's change. The most prominent instance was when the Tenth Doctor and Rose first encountered the Ood in The Impossible Planet. As the Ood were advancing on them the Doctor pulled out his sonic screwdriver and waved it at the Ood in a threatening manner. It lite up and buzzed, but nothing really happened. My first thought was he was only trying to get them to stop by making it seem like he might use it.
But it was not the way it would stay.
When Matt Smith came in as the Eleventh Doctor, we see the first instance of the sonic screwdriver being used as an actual weapon. In Cold Blood the Doctor, on multiple occasions, shoots the weapons out of the Silurian warriors hands. The action is directed at the weapon, and not the Silurians, but it is still actively being used as a weapon. But at this point, it still does not damage to any living entity.
But where the sonic screwdriver finally crossed the line was in Day of the Moon. During the final battle with the Silent, The Doctor and River were fighting back-to-back against the enraged Silent. During the first viewing I thought the Doctor was only waving it around as a distraction while River shot the Silent with her gun.
River: What are you doing?
River: You've got a screwdriver, go build a cabinet.
Doctor: That's really rude.
And right after he says this, he shoots down one of the Silent.
It's at this point that the sonic screwdriver can no longer be called HARMLESS!
NOTE : And this also relates back to The Gentrification of Doctor Who showing how Moffat felt the need to use a typically American shootout scene where the heroes are surrounded by baddies which is, weirdly enough, set in America.